It is well known in the art to synthesize vanadium-phosphorus-oxide (VPO) catalysts for the selective oxidation of C.sub.4 hydrocarbons to maleic anhydride. A recent article which affords an overview of this area of technology is H. S. Horowitz et al., Applied Catalysis, 38 (1988) 193-210 and U.S. Pat. No. 4,677,084 to H. E. Bergna which are each incorporated herein in their entirety.
The VPO catalyst precursor is ordinarily prepared by reducing vanadium pentoxide to vanadium tetraoxide with benzyl alcohol in an isobutanol solution. The benzyl alcohol is oxidized to benzaldehyde. The vanadium tetraoxide is then reacted with phosphoric acid in the presence of tetraethylorthosilicate to form the desired precursor phase having the formula (VO).sub.2 H.sub.4 P.sub.2 O.sub.9. U.S. Pat. No. 4,632,916, at Col. 4, lines 1-6 indicates that various reductants can be employed including isobutanol, benzyl alcohol, and "reduced acids of phosphorus like H.sub.3 PO.sub.3. In the case of using isobutanol and benzyl alcohol, the isobutanol is oxidized more slowly to isobutyraldehyde, and butyral.